The invention relates to a solenoid-valve-controlled fuel injection device, comprising pump and nozzle, for an air-compressing internal combustion engine having a mechanically actuated pump plunger and a pump working space which is bounded by the latter and is in constant communication with a fuel injection line leading to the nozzle, furthermore having an electromagnet, the latter having a stem-like control valve, for controlling a connection of the fuel injection line to a return line for the initiation and ending of injection.
DE 2,742,466 C 2 discloses a solenoid-valve-controlled fuel injection device of this kind in which the beginning of injection and the end of injection are controlled by means of an electromagnet having a control valve for blocking the fuel return and of a control side which interrupts the advance of the fuel to the nozzle needle.
The control valve used here is a pilot valve by which the control slide controlling the advance of the fuel is subsequently influenced. When the fuel feed is completely closed off by the control slide, the fuel delivered is injected at high pump pressure via the nozzle needle lifting off from the valve seat. The end of injection is initiated by opening the pilot valve following discontinuation of the excitation of the electromagnet and simultaneous opening of the control slide.
With a fuel injection device of this type it is virtually impossible to avoid troublesome, harsh combustion noises.
It is therefore an object of the present invention to achieve a reduction of the combustion noises by simple constructional measures on a solenoid-valve controlled fuel injection device comprising pump and nozzle.
This object is achieved by providing an arrangement wherein a control slide acting as inertia piston is guided rotationally fast and so as to be longitudinally displaceable counter to the force of a restoring spring on the valve stem of the control valve and has a control bore via which and via a bore arrangement in the valve stem of the control valve the fuel injection line can be connected to the return line within an injection phase.
Through the use of an inertia piston which is guided slidingly on the control valve of an electromagnet and establishes a connection of the injection line to the fuel return and thus briefly interrupts the injection during one operating cycle per engine cylinder, the injection is divided into a pre- and a main injection. The pre-injection here is a measure to reduce considerably the loud combustion noises occurring in diesel engines. Up to the inertia piston taking effect, a small part of the injection quantity is injected into the combustion chamber and after a very short pause in injection - as soon as the inertia piston is inoperative the remaining principal part of the injection quantity is injected.
Although the division of the injection into a temporally pre- and main injection is known from DE 3,757,731 A1, the discussion there is of a pump in the form of a distributor-type injection pump having a distributor plunger executing rotary and reciprocating movements. The metering of small pre-injection quantities, in particular at high speeds, is problematic, since the combustion chambers of all the cylinders of the internal combustion engine have to be supplied during one rotation of the distributor plunger. The switching times of the solenoid valve must be very short. Also disadvantageous is the ever-increasing interval between pre- and main injection - in terms of crank angle degrees - with increasing speed.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.